On this page: "http://www.englishclub.com/grammar/verb ... e-time.htm", it says that the past perfect continuous conditional can be used to talk about the future, but does not give an option for the past perfect simple conditional: "If I had been working tomorrow, I could not have agreed." - why could one not also say: "If I had worked tomorrow, I could not have agreed." using the third conditional: "http://www.englishclub.com/grammar/verb ... onal_4.htm" - is only the continuous form of the past perfect conditional therefore grammatically correct to use to talk in a future sense?

However, I don't believe that the structure you propose ("If I had worked tomorrow, I could not have agreed") is possible. Even in my most fevered imagination I cannot conceive of a situation in which it could be used.

"I cannot conceive of a situation in which it could be used." - How about someone decides to cancel a work contract and subsequently is offered an opportunity to go on holiday - surely they could then say to the inviter: "If I had worked tomorrow, I could not have agreed."?